How to connect to SSHD inside a Docker container from Windows?

Question

I have a Ruby on Rails environment, and I'm converting it to run in Docker. This is largely because the development machine is a Windows laptop and the server is not. I have the Docker container mainly up and running, and now I want to connect the RubyMine debugger. To accomplish this the recommendation is to setup an SSH server in the container.

https://intellij-support.jetbrains.com/hc/en-us/community/posts/207649545-Use-RubyMine-and-Docker-for-development-run-and-debug-before-deployment-for-testing-

I successfully added SSHD to the container using the dockerfile lines from https://docs.docker.com/engine/examples/running_ssh_service/#build-an-egsshd-image minus the EXPOSE 22 (because it wasn't working with the port mapping in the docker-compose.yml). But the port is not accessible on the local machine

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                                          NAMES
6652389d248c        civilservice_web    "bundle exec rails..."   16 minutes ago      Up 16 minutes       0.0.0.0:3000->3000/tcp, 0.0.0.0:3022->22/tcp   civilservice_web_1

When I try to point PUTTY at localhost and 3022, it says that the server unexpectedly closed the connection.

What am I missing here?

This is my dockerfile

FROM ruby:2.2
RUN apt-get update && apt-get install -y \
    build-essential \
    libpq-dev \
    nodejs \
    openssh-server

RUN mkdir /var/run/sshd
RUN echo 'root:screencast' | chpasswd
RUN sed -i 's/PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config

# SSH login fix. Otherwise user is kicked off after login
RUN sed 's@session\s*required\s*pam_loginuid.so@session optional pam_loginuid.so@g' -i /etc/pam.d/sshd

ENV NOTVISIBLE "in users profile"
RUN echo "export VISIBLE=now" >> /etc/profile

CMD ["/usr/sbin/sshd", "-D"]

RUN mkdir /MyApp
WORKDIR /MyApp
ADD Gemfile /MyApp/Gemfile
ADD Gemfile.lock /MyApp/Gemfile.lock
RUN bundle install
ADD . /MyApp

and this is my docker-compose.yml

version: '2'
services:
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    volumes:
      - .:/CivilService
    ports:
      - "3000:3000"
      - "3022:22"

---

DOCKER_HOST doesn't appear to be an environment variable

docker version outputs the following

Client:
 Version:      17.03.0-ce
 API version:  1.26
 Go version:   go1.7.5
 Git commit:   60ccb22
 Built:        Thu Feb 23 10:40:59 2017
 OS/Arch:      windows/amd64

Server:
 Version:      17.03.0-ce
 API version:  1.26 (minimum version 1.12)
 Go version:   go1.7.5
 Git commit:   3a232c8
 Built:        Tue Feb 28 07:52:04 2017
 OS/Arch:      linux/amd64
 Experimental: true

docker run -it --rm --net container:civilservice_web_1 busybox netstat -lnt outputs

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 0.0.0.0:3000            0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.11:35455        0.0.0.0:*               LISTEN

---

SSHD is now running along side the Rails app, but the recipe that I was working from for setting up the service is not correct for the flavor of Linux that came with my base image https://docs.docker.com/engine/examples/running_ssh_service/#build-an-egsshd-image

The image I'm using is based on Debian 8. Could someone point me at where the example breaks down?

Answer 1

Your sshd process isn't running. That's visible in the netstat output:

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 0.0.0.0:3000            0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.11:35455        0.0.0.0:*               LISTEN

But as user2105103 points out, I should have realized that if I compared your docker-compose.yml with the Dockerfile. You define the sshd command in the image with a Dockerfile line:

CMD ["/usr/sbin/sshd", "-D"]

But then you override your image setting when running the container with the docker-compose command:

command: bundle exec rails s -p 3000 -b '0.0.0.0'

So, the only thing run, as you can see in the netstat, is the rails app listening on 3000. If you need multiple commands to run, then you can docker exec to kick off the second command (not recommended for a second service like this), use a command that launches sshd in the background and rails in the foreground (fairly ugly), or you can consider something like supervisord.

Personally, I'd skip sshd and just use docker exec -it civilservice_web_1 /bin/bash to get a prompt inside the container when you need it.